Tee nut and method of manufacture

ABSTRACT

A Tee nut and method of manufacture is provided which T-nut includes a flange and a hollow barrel extending from the flange. The flange is general circular and has a pair of pawls extending upwardly therefrom, each of which terminates in teeth for engaging a base member. The barrel has an end portion proximal to the flange and a distal end portion. The proximal end portion has internal female threads and the distal end portion has a smooth unthreaded inner surface. The wall thickness of the distal end portion is thinner than the wall thickness of the proximal end portion, and the outer wall diameter is essentially constant for the length of the barrel. 
     The barrel is formed first as an elongate member extending from a strip of material initially having a constant inner diameter and an outer diameter of the proximal portion greater than the outer diameter of the distal portion, with the distal portion having a wall thickness thinner than the wall thickness of the proximal portion. The outer diameter of the distal portion is increased to the same diameter as the outer diameter of the proximal portion while maintaining the same wall thicknesses of both the distal and proximal portions. The internal surface of the proximal portion is threaded with threads terminating at the distal portion and having a lead angle of at least about 80°. 
     The terminal end surface of the distal portion is essentially planar and parallel to a flange.

BACKGROUND OF THE INVENTION

This invention relates generally to a Tee nut and the method ofmanufacturing thereof, and more particularly to a Tee nut formed withimproved pawls and barrel configuration and method of manufacturethereof to provide improved performance of the nut.

BACKGROUND ART

The use of Tee nuts as anchors in wood or plastic or composite or otherbase material into which screws are threaded is well-known in the art.These are especially useful in the manufacturing of furniture.Conventionally Tee nuts include a flange which typically will have pawlsextending therefrom to engage the base wood or other material andprevent rotation of the Tee nut and secure the Tee nut in the material.The Tee nut also has an elongate generally cylindrical barrel which isconventionally threaded internally with female threads. In someinstances the threading extends only partially within the barrel fromthe flange at the proximal end portion to the beginning of the distalend portion with the distal end portion being smooth and often having alarger inside diameter than the proximal end portion.

While the pawls may have several different forms e.g. as shown in U.S.Pat. No. 5,503,596 these various pawl forms have limitations ordrawbacks either in their effectiveness in holding the Tee nut in placeor in the technique of manufacturing the pawls or hampering the feedingof the Tee nuts in automatic feeders.

FIG. 1 shows a side elevational view and FIG. 2 shows a top plan view ofone embodiment of a prior art Tee nut and FIG. 3 shows schematically aproblem known as shingling encountered when the prior art Tee nuts ofFIGS. 1 and 2 are conveyed in a feed track. This as known as shinglingwhich occurs when the flange portion of one Tee nut overrides the flangeportion of an adjacent Tee nut during feeding thus causing jamming orimproper feeding. Moreover, the pawls of the Tee nut shown in FIGS. 1and 2 while particularly useful for inserting the Tee nut in soft wood,if these types of pawls are used in a plastic or dense wood product, theprongs tend not to penetrate the material but to fold over duringinsertion. This can cause the part to spin when the bolt is insertedinto the part. Thus, the prior art Tee nut of FIGS. 1 and 2 has somesignificant problems in feeding and is limited in its use.

FIG. 4 is a side elevational view of another embodiment of a prior artTee nut and FIG. 5 is a plan view of the Tee nut of FIG. 4. FIG. 6depicts somewhat schematically a problem encountered when the Tee nut ofFIGS. 4 and 5 is utilized in an automatic feed track. As can be seen inFIG. 6, the small upwardly projecting pawl can tend to jam in the feedtrack thus preventing proper feed of the Tee nut. Moreover, the pawlconfiguration in the Tee nut of FIGS. 4 and 5 is especially useful inplastic and very dense wood. However, in plywoods or other soft woodsthis pawl, due to its shape and size, tends to rotate when the bolt isinstalled. Thus, the prior art Tee nut shown in FIGS. 4 and 5 haslimitations in its use and significant drawbacks in its ability to befed in an automatic feeding track.

Also, the technique of forming the barrel e.g. as shown in U.S. Pat. No.5,503,596 has several drawbacks and limitations. These include ashallow, and thus less desirable lead angle, and non-uniform barrellengths.

SUMMARY OF THE INVENTION

According to the present invention an improved Tee nut is provided whichincludes a flange and a hollow barrel extending from the flange. Theflange is generally circular in shape and has a pair of pawls extendingupwardly therefrom at spaced locations on the outer periphery of theflange. Each of the pawls terminates in at least two teeth for engaginga base member. The barrel has an end portion proximal to the flange anda distal end portion. The proximal end portion has internal femalethreads and the distal end portion has an essentially smooth innersurface free of threads. Further, the thickness of the wall of thedistal end portion is thinner than the wall thickness of the proximalend portion, and the outer wall diameter is essentially constant for thelength of the barrel thus forming the distal end portion with a largerinner diameter and a thinner wall than the threaded proximal end portionof the barrel.

The invention also includes an improved method of forming the barrelsection of the Tee nut. The barrel is formed first as an elongate barrelmember extending from a strip of material. Thereafter, the barrel isformed to have a constant inner diameter and an outer diameter of theproximal portion greater than the outer diameter of the distal portion,and, with the distal portion having a wall thickness thinner than thewall thickness of the proximal portion. Thereafter, the outer diameterof the distal portion is increased to essentially the same diameter asthe outer diameter of the proximal portion while maintaining the samewall thicknesses of both the distal and proximal portions. Thereafter,the internal surface of the proximal portion is threaded with femalethreads terminating at the distal portion and having a lead angle of atleast about 800 and preferably from about 80° to about 100°.

During the forming process of the barrel, the terminal end surface ofthe distal portion is maintained essentially planar and parallel to aflange to thereby provide a barrel of essentially uniform length aroundthe complete circumference thereof.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of one embodiment of a prior art Teenut;

FIG. 2 is a top plan view of the Tee nut of FIG. 1;

FIG. 3 is a diagrammatic depiction of a malfunction known as shinglingwhen the Tee nuts shown in FIGS. 1 and 2 are utilize a feed track forautomated machinery;

FIG. 4 is a side elevational view of another prior art embodiment of Teenut;

FIG. 5 is a top plan view of the Tee nut of FIG. 4;

FIG. 6 is a diagrammatic representation of a condition resulting injamming when the Tee nut of FIGS. 4 and 5 is utilized in feed track forautomated machinery.

FIG. 7 is a perspective view of a Tee nut according to the presentinvention;

FIG. 8 is a top plan view of the Tee nut of FIG. 7;

FIG. 9 is a longitudinal sectional view taken substantially along theplane designated by the line 9--9 of FIG. 8;

FIG. 10 is a side elevational view taken substantially along the planedesignated by the line 10--10 of FIG. 8;

FIG. 11 is a longitudinal sectional view of the Tee nut of FIGS. 1through 4 inserted into a part with the terminal end of the distalportion crimped over;

FIG. 12 is a side elevational view of another embodiment of a T-nutaccording to this invention; and

FIG. 13 is a longitudinal sectional view, somewhat diagrammatic of fourstations of a progressive die showing the formation of the barrel of theTee nut according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring now to the drawings and to the present FIGS. 7 through 10, aTee nut designated generally as 10 according to the present invention isshown. The Tee nut 10 includes a generally circular flange 12 and abarrel 14 extending upwardly from the flange 12. (The direction"upwardly" as used herein is to designate the direction as depicted inthe drawings, it being understood that the Tee nut can be oriented inany direction in use.) The flange 12 is generally planar and the barrel14 extends generally perpendicular from the flange. The barrel 14 has anend portion 16 proximal to the flange 14 and a distal end portion 18.The barrel 14 also has a through central bore 20. The external diameterof the barrel 14 is essentially constant throughout its entire length.

The proximal end 16 of the barrel 14 has female threads 22 extendingessentially from the flange to the beginning of distal end 16. Thedistal end 18 has a smooth internal surface 24 and terminates in an endwall 26. The end wall 26 is essentially planar and parallel to theflange 12 thus providing a barrel which has a constant length around itscircumference. The wall thickness of the distal end portion 18 issubstantially thinner than the wall thickness of the proximal endportion 16 and at the transition between the threaded portion 22 and thesmooth portion 24 at the beginning of the threads forms a lead angledesignated as α. The lead angle α is at least about 80° and preferablyfrom about 80° to about 100°. The purpose of such particular angle is toassure the proper entry of a screw into the threaded portion as will bedescribed presently.

A pair of pawls 28 are provided which extend upwardly from the flange 12generally parallel to the barrel 14 and preferably are spaced atopposite sides from each other on the flange 12. Each of the pawls 28includes a base portion 30 with a pair of teeth 32 projecting upwardlytherefrom. The teeth are interconnected by a flat interconnectingsurface 34, and each of the teeth terminates generally in a flat end 36.The pawls 28 are formed when the flange 12 is formed and are co-planartherewith. They are then bent up to the position as shown in thedrawings, thus assuring a flange which is essentially round. With thedesign of the pawls 28 and the flange 12 the shortcomings of the priorart Tee nuts shown in FIGS. 1 & 2 and 4 & 5 are overcome. First thedesign of the pawl 28 allows the Tee nut to be used both on relativelysoft wood such as plywood as well as hard wood and plastic. This allowsthe pawls 28 to be inserted into the body of either hard or soft wood orplastic and resist spinning in either type of body. Moreover, the designof the flange 12 and pawls 28 essentially eliminates the problems ofshingling as shown in FIG. 3 with the prior art Tee nut of FIGS. 1 and 2and jamming as shown in FIG. 6 with the prior art Tee nuts of FIGS. 4and 5.

The Tee nut 10 as it is utilized in a part for securing a screw is shownin FIG. 11. As shown in FIG. 11 a portion of a wood or composite orplastic member 40 is shown having a through central bore 42. The centralbore 42 has essentially the same diameter as the outer diameter as thebarrel 14. In a well-known manner the barrel 14 is inserted into thebore 42 and the pawls 28 driven into the member 40 until the flange 12abuts face 43 of the member 40 as shown in FIG. 11. The length of thebarrel 14 is selected such that it is somewhat longer than the length ofthe bore 42 and the distal end 18 is crimped over as shown in FIG. 5 ina well known manner. In order to have the crimp effective it isessential that the end wall 26 be substantially parallel to the flange12 such that the length of the barrel is the same around its entirecircumference. If there is substantial difference in that the one sideof the barrel is significantly too short or too long that side will notcrimp properly and thus the Tee nut will not be restrained in the boreproperly for the reception of the screw. Moreover, if there is varianceof the length of the barrel from side to side when the distal end iscrimped over cracking can occur.

It should also be understood that in some instances where the Tee nut isused, the end of the barrel terminates within the central bore 42. Insuch case the distal portion 18 be flared out in a well known manner.

Also as indicated earlier the lead angle α should be at least about 80°and preferably between about 80° and about 100°. If the angle isshallower or less than about 80° there is a tendency for the screw thatis threaded therein to miss thread or cross-thread or come in at anangle and thus not provide the proper threaded fit between the screw andthe threads 22. This is due to the fact that with an angle of less thanabout 80° the initial part of the thread encountered by the screw is arelatively low percentage of the thread (i.e. less than about one halfof the full thread height) thus causing a misthreading. On the otherhand, it is difficult to manufacture an angle α greater than about 100°.

Referring now to FIG. 12, another embodiment of the Tee nut according tothis invention is shown. In this embodiment pawls 28a are formed withteeth 32a that are pointed rather than flat at the top. This will makethe pawls somewhat easier to insert, but which still will not bend withhard wood or plastic.

Referring now to FIG. 13 various stations of a progressive die 46 areshown together with how they form the shape of the barrel 14. Prior tothe stations in FIG. 13 the formation of the Tee nut with the flange andthe barrel in rough form are conventional such as shown in U.S. Pat. No.5,503,596.

As shown in FIG. 13 four stations 48a, 48b, 48c, and 48d for forming thebarrel into its final shape (except for the threads) are shown. Thestrip with a barrel formed thereon of uniform wall thickness (not shown)formed in a conventional manner is moved from left to right as shown inFIG. 13. At the first station 48a the distal portion of 18 of the barrel14 is formed to have a smaller outer diameter than the proximal portion16 while maintaining a constant inner diameter for the entire length ofthe barrel as shown in station 48a. This means the wall thickness at thedistal portion 18 is thinner than the wall at the proximal portion 16.

At station 48b the first stage of expanding the outer diameter of thedistal portion 18 is performed while maintaining the wall thicknesses ofboth the distal portion and the proximal portion. Station 48c continuesexpanding the outer diameter of the distal portion 18 and at station 48dthe expanding operation is completed to form the final Tee nut havingthe flange 12 and barrel 14 ready for threading. The strip is moved fromleft to right moving the barrel 14 successively from station 48a tostation 48b to station 48c to station 48d and then finally from the dieset in a conventional manner.

The die 46 includes an upper die 58, a lower die 60 and a base plate 62.A stripper plate 64 is provided which is secured to the lower die 60 bymeans of stripper bolts two of which are shown at 68 which bolt 68, eachpass through opening 70 in the base plate 62 opening 72 in lower die 60and threads into opening 74 in the stripper plate 64. Shoulders 76 areformed on the lower die 60, and the springs 78 are disposed in openings72 abutting against the shoulders 76 and the lower portion of stripperplate 64. (The stripper plate 64 is actually formed in two sections onlyone of which is shown to provide a longitudinal path for the barrelduring movement from station to station.)

A plurality of pilots 82a, 82b, 82c, and 82d are provided, one at eachstation which extend through openings 83a, 83b, 83c, and 83d in theupper die 58. A knock-out pin 84 is provide which extends throughopening 86 in the base plate 62 and opening 88 in the lower die 60.Bottom punches 90b, 90c, and 90d extend through openings 92b, 92c, and92d respectively in base plate 62 and openings 94b, 94c and 94drespectively in lower die 60.

The operation of the progressive die is as follows:

A strip with a barrel partially formed thereon moves from left to rightas seen in FIG. 13, and the barrel is formed progressively to its finalshape in stations 48a through 48d. The operation of each station will bedescribed successively, it being understood that the forming operationsare being carried out at the stations simultaneously in the progressivedie 48.

The barrel 14 received from the previous station, (not shown), has aconstant wall thickness slightly larger than the final thickness of theproximal end portion 16 and a length slightly less than the desiredfinal length and is inserted into the lower die 60 at station 48a. Theknock-out pin 84 is inserted into the openings 86 and 88 such that theend of the pin 84 is spaced from the top of the inner die 60 at adistance equal to the desired final length of the barrel 14. The upperdie 58 is then closed and the pilot 82a is driven internally into thecentral bore of the barrel 14 which causes the barrel 14 to be formedwith a distinct proximal end portion 16 and a distinct distal endportion 18 of different wall thickness each being close to equal to thedesired final wall thickness of the respective portion of the barrel.(There may be some slight thinning of these walls during lateroperations.) The outer diameter of the proximal end portion 16 is equalto the desired final outer diameter. Hence, the outer diameter of thedistal portion 18 is less than the desired, final outer diameter thereofwhich desired final outer diameter is equal to the outer diameter of theproximal end 16, so that the outer diameter of the barrel 14 over itsentire length in the final form is uniform.

The strip with the barrel formed as shown in FIG. 48a is then moved tosection 48b. This is accomplished by raising the upper die 58 andraising the knock-out pin 84 to move the bottom of the barrel flush withthe top of the lower die 60. Also, the action of the bolts 68 andsprings 78 causes the stripper plate to move up stripping the strip witha barrel in the varying stages from the lower die. When the limit ofmovement of the stripper plate is reached by blots 68 abutting thebottom of the openings 70, the stripper plate will stop its upwardmovement. As indicated earlier, the stripper plate 64 is actually formedin two sections (a left and right section) which leaves an opening therebetween (not shown) which allows the barrels to move to the nextstation. Of course the pilots 82 have been withdrawn into the upper dieto allow movement of the strip with the partially formed barrels.

As each partially formed barrel moves to the next stage, the upper die58 is again closed. At station 48b this forces the end of the distalportion 18 against shoulder 88b in the lower die and the action of thebottom punch 90b serve to start expanding the outer diameter and theinner diameter of distal section 18 of the barrel 14 while maintainingthe wall thickness thereof with the pilot 82b acting as a guide. Thiswill also assure that the end 26 is parallel to the flange 12. Atstation 48c the barrel which has been partially formed at station 48b isformed further to a point where the outer diameters of the distalportion 18 and proximal portion 16 are approximately equal, and theinner diameter of the distal portion 18 is substantially larger than theinner diameter of the proximal portion 16, with the wall thickness ofthe distal portion 18 still remaining the same. At station 48d the finalsizing and shape of the barrel takes place after which the strip withthe formed barrel 14 is moved from the die.

Thereafter, the shape of the pawls is cut, the pawls are bent up, andthen the part is severed from the strip as is well known in the art.

When formed according to the present invention as shown in FIG. 13, theend wall 24 of the distal portion 18 is essentially flat and parallelwith the flange 12 and thus the length of the barrel 14 is uniformaround its entire circumference which thus aids in the crimpingoperation to provide better holding as described previously. Moreover,when formed according to the present invention the lead angle α aspreviously described can be precisely controlled to be between about 80°and about 100° by controlling the shape of the end of the bottom punches90b, 90c, and especially 90d.

Accordingly, the preferred embodiment of the present invention has beendescribed. With the foregoing description in mind, however, it isunderstood that this description is made only by way of example, thatthe invention is not limited to the particular embodiments describedherein, and that various rearrangements, modifications, andsubstitutions may be implemented without departing from the true spiritof the invention as hereinafter claimed.

What is claimed is:
 1. A Tee nut comprising a flange and a hollow barrelextending from said flange,said flange being substantially circular inshape and having a pair of pawls extending upwardly therefrom, at spacedlocations on the outer periphery of said flange, each of said pawlshaving a base portion and at least two teeth extending therefrom, saidbarrel having an end portion proximal to said flange and a distal endportion, said proximal end portion having internal female threads, saiddistal end portion having a terminal end surface and an essentiallysmooth inner surface free of threads, wherein said first thread in saidproximal end portion is spaced from said terminal end surface of saiddistal end portion by said essentially smooth inner surface and definesa lead angle of between about 80° and about 100°, said inner surface ofsaid distal end portion having a thinner wall thickness than the wallthickness of said proximal end portion.
 2. The invention as defined inclaim 1 wherein adjacent teeth on each pawl are separated by a flatsurface.
 3. The invention as defined in claim 2, wherein said teeth eachterminate in a flat surface.
 4. The invention as defined in claim 2,wherein said teeth each terminate in a pointed configuration.
 5. Theinvention as defined in claim 1 wherein said pawls are equally spacedaround said flange.
 6. The Tee nut of claim 1, wherein said terminal endsurface of said distal end is planar and parallel to said flange aboutits entire circumference.